DRAGON BALL: Sparking! ZERO

You just need to play through the normal path and finish all the episodes in Gokus saga. Playing on reduced difficulty is definitely the best/fastest way to get this as alternate paths are locked in easy mode, so you won't get accidentally side tracked (you can do those paths later).You can make any choices throughout the story as everything is repayable.

Just a tip, I was having some issues and getting the actual ending to the saga in the final battle, I got the What if ending about 5 times for 'winning in a given time'. I think you just need to finish the battle slowly to actually get the proper saga ending.

Alternatively you can use to reduce the difficulty of the game and this automatically prevents any alternate endings to fights so will guarantee the actual saga ending instead of the alternate ending.